Reduction of aromatic nitrogen compounds



United States Patent REDUCTIONOF AROMATIC NITROGEN COMPGUNDS ArmasVictor-Erkkila, Attica, N. Y., assignor to Allied Chemical &.DyeCorporation, New York, N. Y., a corporation of New York No Drawing.Application August 6,1954, Serial No. 448,378

13 Claims. (Cl. 260-143) This inventionv relates to improvements in themethod oi reducing aromatic nitrogen compounds containing mtrogen inzareduci-ble form as a substituent of a benzenenucleus' (that is, as asubstituent of a hydrogen atom forming part of a benzene nucleus) and at'a'higher stage, ofoxi-dation than the hydrazo stage by the action vofmetal alcoholates. It relatesmore particularly to improvements in'suchmethods, andespecially in processes in which the reducingsagent is analkali metal alcoholate, especially anallcali metal methyl'ate andprefera'blymethanol and sodiumv hydroxide, whereby the reduction ispromoted.

Ordinarily, thereduction of nitrobenzene and related aromatic nitrocompounds by means of alkali metal alcoholates is carried out by heatingit with alcoholic caustic -alkali'(e. g., sodium hydroxide and a loweralcohol,

usually methanol) at the boiling point of the mixture while refluxing atatmospheric pressure. Under these conditions, the alkali metalalcoholates are not sufiiciently .strong reducing agents to carry thereduction beyond the 'azoxy stage. As disclosed in U. S. Patents2,645,636 and 2,684,358, this reduction can bepromoted, so as to resultin the formation of reduction products of a lower stage of oxidationthan the azoxy stage, orJto obtain other beneficial results, byincluding in the reduction reaction mixtures naphthoquinoid 'compounds'an-d especially naphthoquinones. and addition products thereof (forexample, with bisulfites, heavy metal salts, etc.) and quinoidhydroxynaphthalene compounds.

The primary object of the present-invention is to:provide additionalreduction promoterswhich, when added to reduction reaction mixtures ofthe type referredto above, will eifect a similar reduction promotingeffect.

A further object of the present invention is to provide improvementsinreductions of the type referred to above whereby-the reducing power ofmetal alcoholate reducing agents and especially of alcoholic causticalkali reducing agents is. enhanced and other .advantages. are secured.

Other objects of the present invention are to provide a process-for :theproduction of aromatic azo compounds in good yields by the reduction ofaromatic nitro compounds, and their reduction products up toand'inclu'ding azoxy compounds, with metal alcoholates undermoderatereaction conditions and in simple apparatus; to provide a process forthe production of aromatic hydrazo compounds-by reduction of .aromaticnitro compounds and other reducible aromatic nitrogen compounds wit-hmetal alcoholates under moderate conditionsandin simple apparatus; andto provide improvements in/thereduction of reducible aromatic nitrogencompounds with metal alcoholates whereby the evolution of hydrogen gasduring the reduction is suppressed.

Additional objects in part will be obvious and ,inpart will appearhereinafter.

According to thepresent invention the foregoing objectsareaccomplishedand other benefits are secured by carrying out thevreduction of the reducible aromatic radical has. as hydrogensubstituents more than one elec- Patented Aug. :27, .1957

nitrogen compound by means-of a metal alcoholate in av reaction mixturein which one or morereduction promoters of a special class have beenincorporated.

The class of reduction promoters employed in accordance with the presentinvention is constituted of certain ice condensed polynuclear dioxycompounds which contain at least 10 nuclear carbon atoms, namely,thosein which one of the nuclei consists of an alicyclic dioxy radicalhaving 6 nuclear carbon atoms and having the oxy substituents in quinoidrelation to each other, at 1east'2 of the nuclear carbon. atoms. of saidalicyclic dioxy radical other than those to which the oxy substituentsare joined being saturated ,carbon atoms and preferably at least 4 ofthe 6 nuclear carbon atoms of said alicyclic dioxyradicalbeingsaturatedcarbon atoms. Said class comprises 1) condensedpolynuclear diketones, such as the condensed nuclear derivatives ofcyclohexandione and ,cyclohexendione in which the carbonyl groups are inquinoid relation, and particularly in 1,2- and 1,4-relation (whetherfreefrom other substituents besides the oxy substituents, or containingadditional substituents wherein one or-m-ore of the hydrogen atoms issubstituted by .anotheratom or radicalfor example, halogen, hydroxyl,

nitro, mercapto, amino, cyano, sulfo, carboxyl, alkyl, alkoxy, etc., butno carbon atom of said alicyclic dioxy tronegative radical); (2)corresponding hydroxy compounds in which one or both of the carbonylgroups of the, above diketones are replaced by one or two groups(whet-her free from other substituents besides the hydroxylgroups orcontaining additional substituents. as above), such as the condensednuclear derivatives of cyclohex-andiol and cyclohexendio'l (condensedpolynuclear secondary alc0h0ls);-and condensed nuclear derivatives ofcyclohexadiendiol, in which the hydroxyl groups are in quinoid relation,and particularly in 1,2-

or 1,4-relation; '(3) addition compounds of such diketones andhydroxy-ketones (for example, with bisulfites, such as those disclosedin U.-S. P. 2,645,636); (4) functional derivatives of such dik-etones,hydroxy-ketones and dihydroxy compounds (for example, imides, oximes,semicarbazones, hydrazones, and esters which are saponifiable jbycaustic alkalis); and :(5) ,ta-utomeric forms of. such .diketones; andhydroxy-ketones capable of isomerizing to suchketones.

Preferred-reduction promoters for use in accordance with the presentinvention arethe 1,2- and 1*,4diOXY- .,naphthanes (diones, diolsandol-ones) and especially the V 1,4-naphthandi0nes and 1,4-naphthandiols.

Thus, saidclass of-condensedpolynuclear dioxy-compounds includes A-naphthantriene-1,4-dione (.2,3-dihydro-1,4-naphthoquinone) A-naphthandiene 1,4 dione (4a,5,8,8a-tetrahydro-1,4-

naphthoquinone) Z-methyl A -naphthandienel ,4-dione-4-oxime(Z-methyldimethyl 2 phenyl 4a,5,8,8a-tetrahydro-1,4-naphth0- quinone)2,3 dimethyl 2 phenylA -naphthantriene-1,4-dione (2,3 dimethyl-Z-phenyl2,3-dihydro -1,4-naphtho-quinone) 5,8 endomethylene-A naphthandiene -1,4 dione (5,8-

methano-4a,5,8,8a-tetrahydro-1,4-naphthoquinone) I 5,8 endoethylene -Anaphthandiene 1,4 dione (5,8-

ethano-4a,5,8,8a-tetrahydro-1,4-naphthoquinone) 6-methoxy-A-naphthandiene-1,4-dione (6-methoxy-4a,5,

8,8a-tetrahydro-1,4-naphthquinone) 2,3,4a,8a-tetrachloro -Anaphthandiene -1,4- dione (2,3,

4a,8a tetrachloro 4a,5,8,8a tetrahydro -1,4-naphthoquinone) Anaphthantriene -1,4 diol l,2,3,4 tetrahydro-l,4-

naphthalenediol) 2-methyl-4-hydroxy -A naphthantriene -I- one(l-hydroxy-4-keto-2-methyl-1,2,3,4-tetrahydonaphthalene) Anaphthantetrene -l,4 diol (2,3-dihydro-1,4-dihydroxynaphthalene)Compounds of this class can be prepared in various Ways. One group ofcompounds particularly useful in accordance with the present inventioncan be obtained by the Diels-Alder reaction of a conjugated diene with a1,4-benzoquinone or 1,4-naphthoquinone. Suitable conjugated dienesinclude 1,3-butadiene, 2-methyl-l,3-butadiene,2-3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene,

2-bromo-l,3-butadiene, 2-phenyl-l,3-butadiene, Z-methyl-2-chloro-l,3-butadiene, 1,3-cyclopentadiene, 2-methyl-1,3- pentadiene,3-chloro-4-methyl-1,3-pentadiene, 1,3-cyclohexadiene and3-chloro-4-methyl-l,3-hexadiene. Those derived from 1,4-benzoquinone andits substitution prodnets are of particular value in view of theirsuperior promotor activity.

I have discovered that said condensed polynuclear dioxy compoundsconstitute highly effective reduction promoters in the reduction ofaromatic nitrogen compounds of the type referred to above by metalalcoholates and especially alkali metal alcoholates.

I have found that the inclusion in the reaction mixture of merely asmall amount of a condensed polynuclear dioxy compound of said type andespecially of a 1,4-naphthadione has a modifying effect upon thereaction as a result of which a number of benefits may be secured.

Thus, as compared with a reduction carried out under the same conditionsbut in the absence of such reduction promoter, the speed of thereduction is increased and/or larly, the inclusion of a reductionpromoter of the above type in the reaction mixture makes possible theproduction of hydrazo compounds from nitro, azoxy and azo compounds bymeans of metal alcoholate reducing agents without requiring the use ofdrastic operating conditions. By their presence, the reduction promoterssuppress almost completely side reactions leading to the evolution ofhydrogen gas during the reduction, thereby greatly increasing the safetyof the reduction process and minimizing waste of the reducing agent.

When no substantial change in the degree of reduction is desired, theinclusion of a reduction promoter of the above type in the reductionreaction medium makes possible the use of milder reaction conditions orthe use of decreased amounts of reducing agent. Thus, in the reductionof an aromatic nitro compound with sodium hydroxide and methyl alcoholthe inclusion of a reduction promoter of the above type in the reactionmixture makes possible the use of a lesser amount of sodium hydroxide,

thereby decreasing the cost of the operation. This result is surprisingbecause the condensed polynuclear dioxy compounds employed in accordancewith the present invention are not quinones but cycloaliphaticcompounds.

In the practice of the present invention, the reducible aromaticnitrogen compound is subjected to the reducing action of a metalalcoholate reducing agent in a reaction mixture in which one or more ofthe promoters referred to above have been incorporated. In the preferredpractice of the invention, wherein the reducible aromatic nitrogencompound is heated with a caustic alkali and an alcohol (preferablysodium hydroxide and methanol) at the boiling point of the reactionmixture, the reduction promoter is preferably mixed with the alcoholand, after adding the caustic alkali and heating, the nitrogen compoundto be reduced is added to the heated mixture. The reduction promoter maybe added to the reaction mixture in various ways and at various times,however, without departing from the scope of the invention.

The reduction promoter can be employed in various amounts. It is afeature of the present invention that the condensed polynuclear dioxycompounds are effective as reduction promoters even when employed insmall amounts. Thus, amounts lying within the range %()0 to & mol ofsuch dioxy compounds per mol of reducible aromatic nitrogen compound areordinarily employed. The minimum amount required to produce asignificant reduction-promoting effect varies with the individualpromoter employed, the nature of the reducible aromatic nitrogencompound, and the reaction conditions. In gen- -eral, a greaterreduction-promoting effect is secured by increasing the amount ofreduction promoter employed and a lesser effect results from decreasingthe amount employed, other reaction conditions being constant.

M Amounts greater than ,4 mol of reduction promoter per mol of reduciblearomatic nitrogen compound usually are not advantageous, although theymay be used if desired, since the additional benefits derived therefromare not of sufficient commercial importance to compensate for theincreased cost of the extra amount of reduction promoter.

The invention will be illustrated by the following specific examples,but it is to be understood that it is not limited to the details thereofand that changes may be made Without departing from the scope of theinvention. The temperatures are in degrees centigrade and the parts areby weight, unless designated as parts by volume in which case the amountsignifies the volume occupied by the same number of parts by weight ofwater at 4 C.

EXAMPLE 1 Forty-three parts of methanol and 1 part of one of thereduction promoters set out in the following Table 1 were charged to aflask equipped with a reflux condenser, stirrer, dropping funnel andthermometer.

Table 1 A. 2,3,4a,5,8,8a hexahydro 1,4 naphthoquinone (Anaphthanene-l,4-dione) B. 2,3-dihydro-1,4 naphthoquinone (A-naphthantricne-1,4-dione) C. 4a,5,8,8a-tetrahydro-1,4 naphthoquinone (A-naphthandiene-1,4-dione) D. 1,4,4a,9a-tetrahydro-anthraquinone(1,3-butadiene reacted with 1,4-naphthoquinone) E. 1,4-naphthoquinoneFifty-six parts of solid sodium hydroxide were then added Table 2Percent of Theoretical Yield Based on Nitrobenzene Charged PromoterHydrazo- Azobenzene Aniline benzene Azoxybenzene None (Control) AEXAMPLE 2 Percent Hydrazobenzene 63 Azobenzene 36.4 Azoxybenzene Aniline0.6

EXAMPLE 3 Part 1.-The procedure of Example 2 was repeated using 63 partsof azobenzene (S. P. 67.6") as the starting material in place of theazoxybenzene. The yields of reduction products, expressed as percent oftheory based on the azobenzene charged, were as follows:

Percent Hydrazobenzene 99.9 Azobenzene 0 Aniline 0.1

Part 2.By way of comparison the following results were obtained whenemploying 1 part of 1,4-naphthoquinone in place of the4a,5,8,8a-tetrahydro-1,4-naphthoquinone under otherwise identicalconditions:

Percent Hydroazobenzene 90 Azobenzene 9.8 Aniline 0.2

As noted above, the invention is not limited to the details of theforegoing illustrative examples, and changes can be made withoutdeparting from the scope of the invention.

Thus, the process is applicable to the reduction of other aromaticnitrogen compounds containing nitrogen in a reducible form as a'substituent in a benzene nucleus, as for example, o-nitrotoluene,m-nitrotoluene, o-nitrochlorobenzene, m-nitrochlorobenzene,p-nitrophenetole, p-nitrobenzoic acid, o-nitrobenzene sulfonic acid, andtheir reduction products. In view of the extensive use of hydrazobenzeneand its o-substituted derivatives (such as o,0-dichlorohydrazobenzene,o,o-'hydrazotoluene, 0,0- hydrazoanisole, 0,0-diethoxyhydrazobenzene,etc.) as intermediates for the manufacture of benzidine and relatedderivatives of benzidine, the process of the present invention is ofspecial value as a means for reducing the cost of manufacturing suchhydrazo compounds from the cor- 6, responding reducible aromaticnitrogen compounds (such as, nitrobenzene and its o-substitutedderivatives and reduction products thereof) in which the nitrogen is ata higher stage of oxidation than the hydrazo stage.

The reduction of aromatic nitro compounds to azoxy compounds (1), ofazoxy compounds to azo compounds (2), and of azo compounds to hydrazocompounds (3) proceed-s according to the following equations, in which Ris an aromatic nucleus:

4RNO 30113011 3NaOH In carrying out the reduction by means of sodiumhydroxide and methanol, it is preferable to employ these reagents inamounts in excess of those theoretically required. Extra methanol overthat theoretically required is generally desirable for use as a solvent,and an additional excess is desirable to counteract the diluting effectof the water generated in accordance with above Equations 1 and 2, whichwould otherwise tend to retard the reaction. An excess of sodiumhydroxide also is desirable since it tends to increase the rate ofreaction.

It is possible to carry the reduction of a particular reducible aromaticnitrogen compound to various stages, depending upon the amounts ofsodium hydroxide and methanol employed, as well as the nature and amountof the particular reduction promoter employed. Thus, it is possible toreduce nitrobenezene to hydrazobenzene in a single reaction mixture.However, it is possible to reduce nitrobenzene to azoxyand/or azobenzenein one reaction mixture, as illustrated in the above examples, and thento isolate and reduce the resulting azoxybenzene and/ or azobenzenetohydrazobenzene with a fresh charge of sodium hydroxide and methanol.

The temperature at which the reaction is carried out also may be variedalthough, in the reduction performed with the aid of alcoholic causticalkali, temperatures at or near the boiling point of the reactionmixture at atmospheric pressure (ordinarily about to are preferred. Atlower temperatures, the reaction is slower, under otherwise similarconditions, and may require an excessively long time to produce the sameresults 'as the preferred temperatures. Conversely higher reactiontemperatures result in a short time cycle but require the use of closedreaction vessels. However, temperatures greatly exceeding though notprecluded, are less desirable; since even in the presence of thereduction promoters they lead to evolution of considerable amounts ofhydrogen gas and formation of primary amines, with consequent loss ofyield of the desired reduction products.

While for economical and simple operation it is preferred to use, as asolvent or diluent of the reaction mixture, an excess of the alcoholemployed for the alcoholate, the invention is not limited thereto. Thus,other solvents and diluents can be employed; for example, the processmay be carried out with amounts of sodium hydroxide and methanol onlyslightly in excess over the amounts theoretically required for thereduction, in a reaction medium containing a sufiicient amount of xyleneor other inert solvent or diluent (such as, benzene, toluene, monoanddichloro-benzenes) to provide a stirrable reaction mass. Further, whileit is simpler to employ as the solvent or diluent an excess of thealcohol functioning as a reducing agent, other alcohols can be employed;also mixtures of alcohols can be used, especially where it is desired tomodify the boiling temperature of the reaction mixture.

As a matter of convenience and for economical operations, the process isgenerally carried out by forming a metal alcoholate in the reactionmixture; for example, by reacting caustic alkali with the alcohol. Ifdesired, however, preformed metal alcoholates may be employed asreducing agents, thereby avoiding the diluting effect of the waterformed as a by-product of the reaction of caustic alkali with thealcohol.

Sodium hydroxide and methanol are employed in the specific examples inview of their relatively lower cost and ready availability. Theinvention is not limited thereto, however, and other alkalis (forexample, potassium hydroxide) and other alcohols (for example, ethylalcohol and the various propyl, butyl and higher alcohols) may beemployed, if desired.

The products of the reduction can be isolated from the reaction mixturesin any suitable manner. Aside from those cases in which the reactionmixture contains an insoluble residue resulting from the presence of thereduction promoter in the reaction mixture, the isolation of thereduction products can be carried out in the usual manner. Thus, forexample, the reaction mixture may be cooled to crystallize the reductionproduct and filtered, and the cake Washed with water to remove alcohol,sodium formate formed as a by-product of the reduction, and sodiumhydroxide.

If desired, the reaction mixture can be steam distilled to remove themethanol (and the aqueous methanol thus obtained can be dehydrated byfractional distillation for reuse in subsequent reactions), and theremaining hot aqueous mass can then be cooled to crystallize thereduction product, which can be separated and washed with water asusual; or, where the product is present in molten form in the hotaqueous mixture, as in the case of azoxyand azobenzenes, the mass can bestratified into an aqueous phase and an oil phase, whereupon the lattercan be readily separated. Ordinarily, the reduction promoters of theabove type are soluble in the aqueous and/or alcoholic layer and areremoved therewith from the reduction product. When the use of thereduction pro moter produces a small amount of insoluble by-product, itmay be removed by filtering the hot mixture prior to thephase-separation, or in any other suitable manner.

I claim:

1. The improvement in the method of reducing an aromatic nitrogencompound containing nitrogen in a reducible form as a substituent of abenzene nucleus at a higher stage of oxidation than the hydrazo stage bythe action of a metal alcoholate, which comprises carrying out thereduction in a reaction mixture in which a condensed polynuclear dioxycompound containing at least nuclear carbon atoms has been incorporated,one of the nuclei of said condensed polynuclear dioxy compoundconsisting of an alicyclic dioxy radical having 6 nuclear carbon atomsand having the oxy substituents in quinoid relation to each other, atleast 2 of the nuclear carbon atoms of said alicyclic dioxy radicalother than those to which the oxy substituents are joined beingsaturated carbon atoms, whereby the reduction of the aromatic nitrogencompound is promoted.

2. A method as defined in claim 1, wherein the aromatic nitrogencompound is reduced to a lower stage of oxidation than the azoxy stage,the alcoholate is sodium methylate and the condensed polynuclear dioxycompound is a condensed dinuclear 1,4-diketone.

3. A method as defined in claim 2, wherein the condensed polynucleardioxy compound is a naphthan-1,4- dione. Y

4. A method as defined in claim 2, wherein the condensed polynucleardioxy compound is a Diels-Alder reaction product of a conjugated dienewith a 1,4-quinone.

5. A method as defined in claim 2, wherein the condensed polynucleardioxy compound is a bisulfite addition compound of a condensed dinucleardiketone.

6. The improvement in the method of reducing a reducible aromaticnitrogen compound selected from the group consisting of nitrobenzene,its ortho-methyl, halogen, methoxy, ethoxy, carboxy and sulfoderivatives, and their reduction products in which the nitrogen is at ahigher stage of oxidation than the hydrazo stage, by the action of ametal alcoholate, which comprises reducing the aromatic nitrogencompound to a lower stage of oxidation than the azoxy stage by reactingthe aromatic nitrogen compound with sodium methylate in a reactionmixture to which a condensed dinuclear diketone having 10 nuclear carbonatoms has been added in an amount at least mol per mol of aromaticnitrogen compound, one of the nuclei of said condensed dinucleardiketone consisting of an alicyclic diketone radical having 6 nuclearcarbon atoms of which at least 4 are saturated carbon atoms and havingthe carbonyl groups in quinoid relation to each other, whereby, thereduction of the aromatic nitrogen compound is promoted.

7. A method as defined in claim 6, which comprises reacting the aromaticnitrogen compound with a reducing mixture of sodium hydroxide andmethanol in a reaction mixture in which a dioxynaphthane having the oxygroups in quinoid relation to each other has been incorporated.

8. A method as defined in claim 7, wherein the dioxynaphthane is a1,4-dioxynaphthane in which the carbon atoms in the 2,3 positions areunsaturated.

9. A method as defined in claim 8, wherein the 1,4-dioxynaphthane is aDiels-Adler reaction product of a 1,3- butadiene with a1,4-benzoquinone.

10. A method as defined in claim 9, wherein the 1,4- dioxynaphthane is A-naphthandiene-1,4-dione.

11. A method as defined in claim 7, wherein the dioxynaphthane is A-naphthantriene-1,4-dione.

12. A method as defined in claim 7, wherein the condensed polynucleardioxy compound is M-naphthanene- 1,4-dione.

13. A method as defined in claim 1 wherein the aromatic nitrogencompound is reduced to a lower stage of oxidation than the azoxy stage,the alcoholate is sodium methylate and the condensed polynuclear dioxycompound is a naphthandiol.

References Cited in the file of this patent UNITED STATES PATENTS2,645,636 Sogn July 14, 1953 2,684,358 Sogn July 20, 1954 2,684,359 SognJuly 20, 1954

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGENCOMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS SUBSTITUENT OF ABENZENE NUCLEUS AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BYTHE ACTION OF A METAL ALCOHOLATE, WHICH COMPRISES CARRYING OUT THEREDUCTION IN A REACTION MIXTURE IN WHICH A CONDENSED POLYNUCLEAR DIOXYCOMPOUND CONTAINING AT LEAST 10 NUCLEAR CARBON ATOMS HAS BEENINCORPORATED, ONE OF THE NUCLEI OF SAID CONDENSED POLYNUCLEAR DIOXYCOMPOUND CONSISTING OF AN ALICYCLIC DIOXY RADICAL HAVING 6 NUCLEARCARBON ATOMS AND HAVING THE OXY SUBSTITUENTS IN QUINOID RELATION TO EACHOTHER, AT LEAST 2 OF THE NUCLEAR CARBON ATOMS OF SAID ALICYCLIC DIOXYRADICAL OTHER THAN THOSE TO WHICH THE OXY SUBSTITUENTS ARE JOINED BEINGSATURATED CARBON ATOMS, WHEREBY THE REDUCTION OF THE AROMATIC NITROGENCOMPOUND IS PROMOTED.